Note: Descriptions are shown in the official language in which they were submitted.
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
1
A POLYMER PRODUCT FOR IMPROVING RETENTION OF
HYDROPHOBIC INTERNAL SIZING AGENTS IN MANUFACTURE OF
PAPER OR BOARD
Field of the invention
The present invention relates to a manufacture of paper or board and more
specifically to paper or board sizing. The invention relates a method for a
manufacturing paper or board and to an internal sizing system for providing
improved retention of hydrophobic internal sizing agents.
Background of the invention
Sizing is used during paper or board manufacture to reduce the paper's or
board's tendency to absorb liquid. One goal of sizing may also be to allow
inks and paints to remain on the surface of the paper or board and to dry
there, rather than be absorbed into the paper or board. To reach these goals
various sizing agents have been developed and commonly used in the
manufacture of paper or board. Sizing agents may be conducted at the wet-
end of papermaking process or a suitable coating may be applied on dried
paper. Wet-end sizing agents may also have other functionalities than
increasing resistance to water penetration only. Wet-end sizing agents may
also decrease dusting, control spread of inks, improve dewatering, improve
paper quality among other functions.
Sizing at the wet-end of papermaking process uses internal sizing agents.
Desired internal sizing agents have some basic characteristics such as high
hydrophobicity, good retention on fibres, and uniform distribution throughout
the fibre surfaces. Rosin resins are one of the internal sizing agents and
effective for acidic papermaking conditions. Alkenyl succinic anhydride (ASA)
and alkyl ketene dimer (AKD) have been specifically developed as internal
sizing agents for basic or neutral papermaking conditions. ASA reacts with
cellulose hydroxyl readily and develops an instant on-machine sizing effect.
Fast sizing development achieved with ASA ensures that the application of
subsequent surface chemicals remain mostly on the surface of the paper
web. AKD reacts relatively slowly with cellulose and the sizing development
may take days or weeks after drying.
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
2
A controlling of the retention of the internal sizing agents onto fibres is
important since otherwise they may accumulate in the process waters and/or
form deposition on the process surfaces. Formed deposits may cause quality
defects and also web breakages and so affect productivity on paper or board
machine. Therefore, methods for improving retention of hydrophobic internal
sizing agents are under the continuous interest.
Most paper mills using ASA use cationic starch as emulsifying agent.
Cationic starch has been shown to promote ASA sizing efficiency and greater
.. starch dosages will typically lead to higher sizing level. However, starch
is
often not a desired constituent in papermaking mills because it may lead to
excessive biological growth and deposit issues. Therefore, there is a need for
solutions which may decrease an amount of the cationic starch used in the
sizing while maintaining or even improving the internal sizing efficiency.
In papermaking industry one essential parameter is also cost and adaptability
with the existing methods and machinery. Therefore, novel methods for
requiring smaller amounts for internal sizing agents and decreasing costs are
also under the continuous interest. Any new method should be economic to
use and should require only minimal adaptions to the existing systems.
Summary of the Invention
It is an object of the present invention to reduce or even eliminate the above-
mentioned problems appearing in prior art.
An object of the present invention is especially to improve the fixation of
the
hydrophobic internal sizing agents onto the fibres.
A further object of the present invention to provide a method for
manufacturing paper or board which requires smaller amount of the
hydrophobic internal sizing agents to provide required 00BB60 value of the
paper of board, i.e. properties to resist penetration and retention of
moisture.
These objects are attained with the invention having the characteristics
presented below in the characterising parts of the independent claims. Some
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
3
preferred embodiments of the invention are presented in the dependent
claims.
The features recited in the dependent claims and the embodiments in the
description are mutually freely combinable unless otherwise explicitly stated.
The exemplary embodiments presented in this text and their advantages
relate by applicable parts to the method, the treatment system, the use as
well as to the paper or board according to the invention, even though this is
.. not always separately mentioned.
An internal sizing system according to the invention for manufacturing of
paper or board comprises
- a hydrophobic internal sizing agent as a first component selected from
the group consisting of alkenyl succinic anhydride (ASA), alkyl ketene
dimer (AKD), rosin sizes, and any combination thereof, and
- a water-soluble polymer product comprising amphoteric
polyacrylamide as a second component, which amphoteric
polyacrylamide has neutral or cationic net charge at pH 7, a weight-
average molecular weight of 700 000 ¨ 18 000 000 g/mol and a total
ionicity of 4 ¨ 28 mol-`)/0 and which amphoteric polyacrylamide
comprises a crosslinker less than 0.002 mol-`)/0,
wherein the first component and the second component are provided as
separate components or as a combination of the first component and the
second component.
A method according to the invention for manufacturing paper or board, where
a fibre web is formed from an aqueous suspension of fibres, the method
comprising:
- providing an aqueous fibre suspension;
- optionally diluting the aqueous fibre suspension;
- delivering the aqueous fibre suspension to a headbox, draining the
aqueous
fibre suspension on a wire screen to form a wet web of paper or paperboard,
and
.. - pressing and drying the wet web to obtain a web of paper or board,
wherein a hydrophobic internal sizing agent selected from the group
consisting of alkenyl succinic anhydride (ASA), alkyl ketene dimer (AKD),
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
4
rosin sizes, and any combination thereof, and a water-soluble polymer
product comprising amphoteric polyacrylamide having neutral or cationic net
charge at pH 7, a weight-average molecular weight of 700 000 ¨ 18 000 000
g/mol and a total ion icity of 4 ¨ 28 mol-`)/0 and comprising a crosslinker
less
than 0.002 mol-`)/0, are added at least to a fraction of the fibre suspension
as
a combination or separate components.
According to the present invention, a water-soluble polymer product
comprising amphoteric polyacrylamide, which has neutral or cationic net
charge at pH 7, a weight-average molecular weight of 700 000 ¨ 18 000 000
g/mol and a total ionicity of 4 ¨ 28 mol-`)/0 and which amphoteric
polyacrylamide comprises a crosslinker less than 0.002 mol-`)/0, is used for
improving retention of the hydrophobic internal sizing agents selected from
the group consisting of alkenyl succinic anhydride (ASA), alkyl ketene dimer
(AKD), rosin sizes, and any combination thereof in manufacture of paper or
board, where a fibre web is formed from an aqueous suspension of fibres.
A paper or board product according to the present invention comprising the
specified internal sizing system according to the present invention. The paper
of board product according to the present invention is preferably obtained by
the inventive method or by the inventive use of a specified water-soluble
amphoteric polyacrylamide.
Now it has been surprisingly found out that the water-soluble polymer
product, which comprises a specified amphoteric polyacrylamide, improves
retention of the hydrophobic internal sizing agents to be added to a fibre
suspension. The present invention relates also to improved sizing efficiency,
which is attributed at least by amphoteric polyacrylamide's ability to improve
retention of the hydrophobic internal sizing agents to the paper or board web.
A further improvement in sizing efficiency may originate from amphoteric
polyacrylamide's ability to improve retention of fines to the paper or board
web simultaneously with the hydrophobic internal sizing agents, as these are
typically associated with the fines present in the fibre suspension. Further,
the improved retention of hydrophobic internal sizing agents and the fines
reduces their accumulation in process waters, such as white water. It is
assumed that the amphoteric polyacrylamide successfully fixes, i.e. attaches
or associates, the hydrophobic internal sizing agent(s) onto the fibres and
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
thus to the paper or board web, thereby also reducing their accumulation and
deposition in the process surfaces and/or waters. This may be observed by
improved runnability of the paper or board machine since web breakages
may be avoided when the internal sizing agents and/or fines are not
5 accumulated in the process waters and/or form deposition on the process
surfaces. The improved sizing efficiency may also be attributed by improved
shear resistance of the size fixation assisted by the amphoteric
polyacrylamide.
The improved fixation of hydrophobic internal sizing agents may even provide
improved control of migration of the hydrophobic internal sizing agents in the
paper or board, thereby benefiting the sizing performance.
The improved retention achieved by the method according to the invention
makes possible to achieve target Cobb60 value of the paper or board product
with lower amount of the hydrophobic internal sizing agents, whereby
significant cost savings is also achieved. By using the amphoteric
polyacrylamide, the amount of cationic starch in the hydrophobic internal size
formulation may also be reduced or even eliminated, thereby reducing the
need for biocides, and improving quality of circulating waters. When cationic
starch is used in the hydrophobic internal size formulations, the amphoteric
polyacrylamide may provide the additional benefit of improved retention of
the cationic starch thereby avoiding its accumulation to the water
circulation.
In a preferred embodiment of the invention, the paper or board product has at
least 5 %, preferably at least 8 %, more preferably at least 10 % lower
Cobb60 value compared to an otherwise similar paper or board not
comprising the second component of the internal sizing system. The paper or
board product according to an embodiment of the invention has a
predetermined Cobb60 value and comprising at least 5 %, preferably at least
10 %, more preferably at least 15 % less of the first component of the
internal
sizing system, compared to an otherwise similar paper or board having the
same predetermined Cobb60 value and not comprising the second
component of the internal sizing system.
Further, the total ionicity, and especially cationicity, of the specified
amphoteric polyacrylamide is moderate or even low, whereby the risk of
overcationisation of the paper or board making process is also reduced.
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
6
The internal sizing system according to the present invention has been
observed to function in a large pH range, both acidic and neutral or alkaline
conditions.
Detailed description of the invention
According to the context of the present application, the term "hydrophobic
internal sizing agents" is used to encompass al kenyl succinic anhydride
(ASA), alkyl ketene dimer (AKD), rosin sizes, and any combinations thereof.
In the present invention, at least one hydrophobic internal sizing agent is
used in combination with a specified amphoteric polyacrylamide.
In the context of the present application the term "amphoteric polyacrylamide"
denotes a polyacrylamide where both cationic and anionic units are present
in an aqueous solution at pH 7. Amphoteric polyacrylamide is obtained by
copolymerisation of acrylamide or methacrylamide together with both anionic
and cationic monomers. Preferably amphoteric polyacrylamide is obtained by
copolymerisation of acrylamide together with both anionic and cationic
monomers.
The term "water-soluble" is understood in the context of the present
application that the polymer product, and consequently the amphoteric
polyacrylamide, is fully miscible with water. When mixed with excess of
water, the amphoteric polyacrylamide in the polymer product is preferably
fully dissolved and the obtained polymer solution is preferably essentially
free
from discrete polymer particles or granules. Excess of water means that the
obtained polymer solution is not a saturated solution.
The amphoteric polyacrylamide has neutral or cationic net charge at pH 7.
Neutral net charge means that at pH 7 the charges of the anionic and
cationic charged units present in the polyacrylamide cancel out each other,
whereby the amphoteric polyacrylamide has a neutral net charge. In the net
cationic embodiment, the amphoteric polyacrylamide has more cationic
charges than anionic charges at pH 7, whereby the amphoteric
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
7
polyacrylamide has a cationic net charge. According to one embodiment 50 ¨
95 %, preferably 60 ¨ 90 %, more preferably 70 ¨ 85 %, of the charged units
in the amphoteric polyacrylamide are cationic. Thus, according to one
preferable embodiment the amphoteric polyacrylamide has a net cationic
charge as measured at pH 7. This means that the net charge of the
amphoteric polyacrylamide remains positive, even if it contains anionic units.
The net charge of the amphoteric polyacrylamide is calculated as the sum of
the charges of the cationic and anionic units present. The net cationicity of
the amphoteric polyacrylamide provides improved interaction between the
amphoteric polyacrylamide and all anionic components present in the fibre
suspension, most importantly with fibres. Also, the fixation of the
hydrophobic
internal sizing agents may be improved, especially when they are associated
with the anionic fines present in the fibre suspension.
According to one embodiment the amphoteric polyacrylamide in the polymer
product comprises 3 ¨ 25 mol-`)/0, preferably 3 ¨ 20 mol-`)/0, more preferably
4
¨ 12 mol-`)/0, of structural units derived from cationic monomers. According
to
one embodiment the amphoteric polyacrylamide in the polymer product
comprises 0.5 ¨ 6 mol-`)/0, preferably 1 ¨5 mol-`)/0, more preferably 1 ¨ 3
mol-
%, of structural units derived from anionic monomers.
The amphoteric polyacrylamide has a weight-average molecular weight of
700 000 ¨ 18 000 000 g/mol. When the amphoteric polyacrylamide is
prepared by gel polymerisation process the weight-average molecular weight
of the polyacrylamide is preferably 3 500 000¨ 18 000 000 g/mol. According
to one preferable embodiment the amphoteric polyacrylamide has the weight-
average molecular weight in the range of 1 000 000 ¨ 18 000 000 g/mol,
preferably 2 500 000 ¨ 18 000 000 g/mol, more preferably 3 000 000 ¨
18 000 000 g/mol, even more preferably 3 500 000 ¨ 11 000 000 g/mol or 3
500 000 ¨ 8 000 000 g/mol. The molecular weight of the amphoteric
polyacrylamide has an impact on its behaviour and performance. It has been
observed that when the weight-average molecular weight of the amphoteric
polyacrylamide is 700 000 g/mol or more, preferably 1 000 000 g/mol or
more, there is improved fixing of hydrophobic internal sizing agents, to the
fibres. By raising the weight-average molecular weight of the amphoteric
polyacrylamide, the further improvement of flocculation, retention and
drainage may be achieved. However, it has also been observed that when
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
8
the weight-average molecular weight is at most 18 000 000 g/mol, the fibres
are more evenly spaced, there is reduced risk of over-flocculation, so the
formation of the web is not disturbed, even with higher polymer dosages. The
weight-average molecular weight in the range of 3 500 000 ¨ 11 000 000
g/mol or 3 500 000 ¨ 8 000 000 g/mol provides the improvement of
flocculation, retention and drainage with the reduced risk of over-
flocculation,
even at higher dosage levels. This may be also due to the presence of both
anionic and cationic charges, so amphoteric polymers are capable of forming
loops in papermaking fibre suspension, especially in neutral papermaking
pH, thereby preventing too extensive flocculation that could spoil the
formation of the formed web.
The amphoteric polyacrylamide may have an intrinsic viscosity in the range
of 2.7 ¨ 27 dl/g, which approximately corresponds a weight-average
molecular weight of 700 000¨ 18 000 000 g/mol. According to one preferred
embodiment the intrinsic viscosity of the amphoteric polyacrylamide may be
in the range of 3.5 ¨ 27 dl/g, preferably 6.7 ¨ 27 dl/g, more preferably 7.5 ¨
27 dl/g, even more preferably 8.5 ¨ 19 dl/g, such as 8.5 ¨ 15.2 dl/g. The
intrinsic viscosities reflect the molecule size and may be calculated into
weight-average molecular weights as explained hereinafter.
The value "weight-average molecular weight" is in the present context used
to describe the magnitude of the polymer chain length. Weight-average
molecular weight values are preferably calculated from intrinsic viscosity
results measured in a known manner in 1N NaCI at 25 C by using an
Ubbelohde capillary viscometer. The capillary selected is appropriate, and in
the measurements of this application an Ubbelohde capillary viscometer with
constant K=0.005228 was used. The average molecular weight is then
calculated from intrinsic viscosity result in a known manner using Mark-
Houwink equation [ri]=K.Ma, where [ri] is intrinsic viscosity, M molecular
weight (g/mol), and K and a are parameters given in Polymer Handbook,
Fourth Edition, Volume 2, Editors: J. Brandrup, E.H. Immergut and E.A.
Grulke, John Wiley & Sons, Inc., USA, 1999, p. VII/11 for poly(acrylamide).
Accordingly, value of parameter K is 0.0191 ml/g and value of parameter "a"
is 0.71. The average molecular weight range given for the parameters in
used conditions is 490 000 ¨ 3 200 000 g/mol, but the same parameters are
used to describe the magnitude of molecular weight also outside this range.
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
9
pH of the polymer solutions for intrinsic viscosity determination is adjusted
to
2.7 by formic acid to avoid probable poly-ion complexation of amphoteric
polyacrylamides.
The amphoteric polyacrylamide has a total ionicity of 4 ¨ 28 mol-`)/0.
According to one preferable embodiment the total ionicity of the amphoteric
polyacrylamide is in the range of 4 ¨ 25 mol-`)/0, preferably 5 ¨ 20 mol-`)/0,
more preferably 6 ¨ 15 mol-`)/0, even more preferably 6 ¨12 mol-`)/0. The
amphoteric polyacrylamide in the polymer product may comprise at least 72
mol-`)/0, preferably at least 75 mol-`)/0 structural units derived from
acrylamide
and/or methacrylamide monomers, and at most 28 mol-`)/0, preferably at most
25 mol-`)/0 of structural units originating from anionic and cationic
monomers.
Total ionicity includes all structural units having ionic charge in the
amphoteric polyacrylamide, most of the charged units originating from the
ionic monomers but including also other charged units originating from chain
termination agents or the like. It has been observed that it is beneficial
when
the total ionicity of the polymer is at most 20 mol-`)/0, especially when the
weight-average molecular weight of the polymer is 700 000 ¨ 18 000 000
g/mol, or preferably 3 500 000 ¨ 11 000 000 g/mol. Higher ionicity, especially
cationicity, could cause overcationisation when the polymer product is used
in increased dosages. Thus, the relatively low ionicity of the amphoteric
polyacrylamide enables the use of increased polymer product dosages to
fibre suspensions, even if the pulp has a zeta potential values close to zero.
The ionicity of the amphoteric polyacrylamide can be optimised in view of
avoiding the zeta potential problems in the stock, i.e. shifting of the zeta
potential of the pulp to positive values.
According to one preferable embodiment the amphoteric polyacrylamide is a
linear polyacrylamide. In other words, the amphoteric polyacrylamide is
unbranched and preferably not crosslinked. In the polymerisation the amount
of cross-linker is less than 0.002 mol-`)/0, preferably less than 0.0005 mol-
`)/0,
more preferably less than 0.0001 mol-`)/0 for providing a substantially linear
amphoteric polyacrylamide. According to one embodiment the polymerisation
is completely free of cross-linker. When the amphoteric polyacrylamide
comprises less than 0.002 mol-`)/0 of crosslinker, the amphoteric polymer
dissolves more quickly, and the possibility for insoluble polymer particles
after dissolution is effectively reduced. In this way the whole dosage of
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
amphoteric polyacrylamide is effective for flocculation, retention and
drainage. Presence of insoluble polymer particles may also reduce the
quality of the produced paper or board. Additionally, when the amphoteric
polyacrylamide comprises less than 0.002 mol-`)/0 of crosslinker, the polymer
5 chains may remain more extended, even when in looped conformation,
and/or the charged groups may be more accessible for interactions, thereby
improving flocculation and retention.
According to one embodiment the cationic units in the amphoteric
10 polyacrylamide originate from monomers selected from 2-
(dimethylamino)ethyl acrylate (ADAM), [2-
(acryloyloxy)ethyl]
trimethylammonium chloride (ADAM-CI), 2-(dimethylamino)ethyl acrylate
benzylchloride, 2-(dimethylamino)ethyl acrylate dimethylsulphate, 2-
d imethyl aminoethyl methacryl ate (MADAM), [2-(methacryloyloxy)ethyl]
trimethylammonium chloride (MADAM-CI), 2-dimethylaminoethyl
methacrylate dimethylsulphate, [3-(acryloylamino)propyl] trimethylammonium
chloride (APTAC), [3-(methacryloylamino)propyl]
trimethylammoniu m
chloride (MAPTAC) and diallyldimethyhammonium chloride (DADMAC).
Quaternary amines are preferred cationic monomers because their charge is
not pH dependent. More preferably the cationic monomer is [2-
(acryloyloxy)ethyl] trimethylammonium chloride (ADAM-CI).
According to one embodiment the anionic units in the amphoteric
polyacrylamide originate from monomers selected from unsaturated mono- or
dicarboxylic acids or sulphonic acids, preferably from unsaturated
monocarboxylic acids or sulphonic acids, such as (meth)acrylic acid, and/or
2-acrylamido-2-methylpropane sulfonic acid (AMPS). While referring to the
acid form, it is meant to cover also other forms, such as salt forms of said
unsaturated mono- or dicarboxylic acids and sulphonic acids. Most preferably
the anionic monomer is acrylic acid or methacrylic acid or salts thereof.
The amphoteric polyacrylamide of the polymer product may be obtained by
gel polymerisation. According to one embodiment, this preparation process
may use a reaction mixture comprising non-ionic monomers, such as
acrylamide, and the charged anionic and cationic monomers. The monomers
in the reaction mixture are polymerised in presence of initiator(s) by using
free radical polymerisation. The temperature in the beginning of the
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
11
polymerisation may be less than 40 C, sometimes less than 30 C.
Sometimes the temperature in the beginning of the polymerisation may be
even less than 5 C. The free radical polymerisation of the reaction mixture
produces amphoteric polyacrylamide, which is in gel form or highly viscous
liquid. After the gel polymerisation, the obtained amphoteric polyacrylamide
in gel form is comminuted, such as shredded or chopped, as well as dried,
whereby a particulate polymer product is obtained. Depending on the used
reaction apparatus, shredding or chopping may be performed in the same
reaction apparatus where the polymerisation takes place. For example,
polymerisation may be performed in a first zone of a screw mixer, and the
shredding of the obtained polymer is performed in a second zone of the said
screw mixer. It is also possible that the shredding, chopping or other
particle
size adjustment is performed in a treatment apparatus, which is separate
from the reaction apparatus. For example, the obtained hydrosoluble, i.e.
water-soluble, polymer may be transferred from the second end of a reaction
apparatus, which is a belt conveyor, through a rotating hole screen or the
like, where it is shredded or chopped into small particles. After shredding or
chopping the comminuted polymer is dried, milled to a desired particle size
for obtaining polymer product in a particle form and packed for storage and/or
transport.
According to one embodiment of the invention the amphoteric polyacrylamide
is obtained by gel polymerisation process, where the content of monomers in
the reaction mixture at the start of the polymerisation is at least 29 weight-
%,
preferably at least 30 weight-%, more preferably at least 32 weight-%.
According to one embodiment the amphoteric polyacrylamide content in the
polymer product is at least 25 weight-%, preferably at least 60 weight-%. A
polymer product having lower polymer content, e.g. obtained by solution
polymerisation, has the advantage of easier dilution or dissolution to the
concentration of use. A polymer product having a higher polymer content,
e.g. obtained by gel polymerisation, emulsion polymer product obtained by
emulsion polymerization, optionally dehydrated, or dispersion polymer
product obtained by dispersion polymerization, optionally dehydrated, is more
cost efficient in view of the logistics of the product. A high polymer content
has the additional benefit of improved microbial stability. For example, when
the polymer content of the polymer product is at least 60 weight-%, which is
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
12
typical for a polymer product obtained by gel polymerisation, microbial
activity
is reduced, and the polymer product is more stable even in warm climate and
for long storage periods.
According to one preferable embodiment of the invention the amphoteric
polyacrylamide content in the polymer product is in the range of 60 ¨ 98
weight-%, preferably 70 ¨ 98 weight-%, more preferably 75 ¨ 95 weight-%,
even more preferably 80 ¨ 95 weight-%, sometimes even more preferably 85
¨ 93 weight-%. Because the amphoteric polyacrylamide content of the
polymer product may be high, naturally the amount of active amphoteric
polyacrylamide is also high. This has a positive impact on transport and
storage costs of the polymer product. Moisture content of the polymer
product is typically 5-12 weight-%.
According to one preferable embodiment the polymer product comprising
amphoteric polyacrylamide is in particle form. In the context of the present
application the term "particle form" denotes discrete solid particles or
granules. According to one embodiment of the invention the polymer product
comprises particles or granules of amphoteric polyacrylamide, which have an
average particle size of < 2.5 mm, preferably < 2.0 mm, more preferably <
1.5 mm. These particles are obtained by subjecting the amphoteric
polyacrylamide obtained by gel polymerisation to mechanical comminution,
such as cutting, milling, shredding, chopping or the like.
According to one embodiment of the present invention the solids content of
the polymer product in particle form may be > 80 weight-%, preferably > 85
weight-%, more preferably in the range of 80 ¨ 97 weight-%, even more
preferably 85 ¨ 95 weight-%. The high solids content is beneficial in view of
storage and transport properties of the polymer product.
When used, the water-soluble polymer product comprising the amphoteric
polyacrylamide is usually dissolved into water and/or diluted, whereby an
aqueous treatment solution is obtained. As used herein, by dissolving in
water to obtain an aqueous treatment solution, it is meant to cover both
dissolving and diluting. The amphoteric polyacrylamide content of the said
aqueous treatment solution may be 0.1 ¨ 4 weight-%, preferably 0.3 ¨ 3
weight-%, more preferably 0.5 ¨ 2 weight-%. According to one embodiment
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
13
the water-soluble polymer product comprising amphoteric polyacrylamide is
dissolved in water having pH 2.5 ¨ 6.5, preferably 2.5 ¨ 6, such as 2.5 ¨ 5.5,
more preferably 2.5 ¨ 5 to obtain the aqueous treatment solution of the
polymer product comprising amphoteric polyacrylamide. The suitable pH may
be adjusted e.g. by adding an acid, or base. Using this slightly acidic pH in
polymer dissolution the amphoteric polyacrylamide maintains its full
functionality. Additionally, using this pH range some undesired effects on the
hydrophobic internal sizing agent, such as hydrolysis thereof, may be
avoided or slowed down, especially when the hydrophobic internal sizing
agent is emulsified and/or stabilized with the amphoteric polyacrylamide. In
this respect the pH value of the hydrophobic internal sizing agent emulsion,
especially of ASA emulsion, is advantageously in the range of 3 ¨ 6,
preferably 3 ¨ 5, more preferably 3 ¨ 4.
According to the present invention, the hydrophobic internal sizing agent is
selected from the group consisting of alkenyl succinic anhydride (ASA), alkyl
ketene dimer (AKD), rosin sizes, and any combination thereof. In a preferred
embodiment of the invention, a hydrophobic internal sizing agent is alkenyl
succinic anhydride (ASA).
An internal sizing system according to an embodiment of the present
invention comprises a water-soluble polymer product and a hydrophobic
internal sizing agent in a weight ratio of 1:15 ¨ 1.5:1, preferably 1:10 ¨
1:2.
Higher amounts of the water-soluble polymer product are not expected to be
cost-efficient and to provide substantial further benefit in internal sizing,
and
lower amounts may be inadequate for achieving the desired sizing
specifications.
According to the invention the polymer product comprising a specified
amphoteric polyacrylamide is used for improving retention of the hydrophobic
internal sizing agent(s). An internal sizing system according to the present
invention comprises a hydrophobic internal sizing agent as a first component
and a polymer product comprising a specified amphoteric polyacrylamide as
a second component, wherein the first component and the second
component are provided as separate components, or as a combination of the
first component and the second component. According to the invention at
least one hydrophobic internal sizing agent and the polymer product
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
14
comprising a specified amphoteric polyacrylamide are added to the fibre
suspension separately or a combination of them. In the context of the present
application the combination of the components may refer to a mixture of the
components, or simultaneous addition of the components to a fibre
suspension, or a combination in which a first component is emulsified and/or
stabilized with a second component. The embodiments of the invention are
disclosed more detailed below.
An addition point, a way of the addition and the amounts to be added are
.. dependent on e.g. the hydrophobic internal sizing agent, paper or board to
be
manufactured and fibre suspension.
In the present context, rosin resins refer to various types of the rosin
sizes,
such as tall oil rosin and gum rosins. Examples of rosin resins include
fortified rosin sizes, such as rosins at least partially reacted with maleic
anhydride and/or fumaric acid, and cationic rosin sizes, such as rosin soap
sizes. The rosin resins are typically available in a usable form. Also, AKD is
typically available in a usable dispersion. Whereas ASA has to be emulsified
on-site due to its high reactivity by using a separate emulsifying equipment
and it is typically used directly without any intermediate storage.
A hydrophobic internal sizing agent may be formulated, i.e. emulsified and/or
stabilized with cationic starch, a specified amphoteric polyacrylamide
according to the invention (a second component of the internal sizing system)
or any combination of them. Also, other polymers, such as polyamine may be
used.
According to an embodiment of the invention, a first component, i.e. a
hydrophobic internal sizing agent may be formulated with cationic starch, i.e.
a hydrophobic internal sizing agent may be emulsified and/or stabilized with
cationic starch. ASA is usually emulsified and stabilized with cationic starch
at the paper mill just prior dosage, wherein a cationic starch is used as an
emulsifying agent. The obtained ASA emulsion may be added to a fibre
suspension. AKD and rosin resins are typically stabilized with cationic
starch,
.. earlier at chemical mill since they can be stored and delivered in the
stabilized form. Correspondingly, the obtained AKD and rosin resin
dispersions or emulsions may be added to a fibre suspension. A dosage
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
point may depend on the manufacturing process and the paper or board to
be manufactured.
According to an embodiment of the present invention the combination of the
5 first and
a second component has formed by emulsifying the first component,
i.e. a hydrophobic internal sizing agent with the aqueous treatment solution
of
the second component. All cationic starch or at least part of a cationic
starch
may be replaced with the treatment solution of the polymer product
comprising amphoteric polyacrylamide. According to an embodiment of the
10 invention, an amount of the amphoteric polyacrylamide may be 5 ¨ 40
weight-%, preferably 15 ¨ 20 weight-% of the hydrophobic internal sizing
agent, calculated as dry. When a part of cationic starch is replaced by the
treatment solution of the polymer product comprising amphoteric
polyacrylamide, then a dose of the amphoteric polyacrylamide may be e.g. 3
15 ¨ 20
weight-% of the hydrophobic internal sizing agent, calculated as dry. If
starch is replaced with the amphoteric polyacrylamide, the formulation is less
vulnerable to microbial degeneration, and also less starch ends up into
circulating waters of the papermaking system. Also in this embodiment, ASA
is emulsified and stabilized at the paper mill just prior dosage, whereas AKD
and rosin resins may be formulated already earlier at chemical mill. The
obtained emulsion or dispersion may be added to a fibre suspension.
In one preferred embodiment of the invention the internal sizing system is a
combination of the alkenyl succinic anhydride (ASA) and a polymer product
comprising specified amphoteric polyacrylamide, which combination has
formed by emulsifying ASA with the aqueous treatment solution of the
polymer product comprising amphoteric polyacrylamide. In this embodiment
ASA is emulsified with the aqueous treatment solution of the polymer product
comprising amphoteric polyacrylamide instead of a cationic starch or at least
part of the cationic starch is replaced with the aqueous treatment solution of
the polymer product comprising amphoteric polyacrylamide as disclosed
above. In that case, both ASA and the amphoteric polyacrylamide are
present in the emulsion of the ASA to be added to the fibre suspension. In
this embodiment, no separate addition of the aqueous treatment solution of
the polymer product comprising amphoteric polyacrylamide is required, but it
is possible to add separately a hydrophobic internal sizing agent, such as
ASA formulated with the amphoteric polyacrylamide and the aqueous
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
16
treatment solution of the polymer product comprising amphoteric
polyacrylamide to a fibre suspension.
A viscosity of the cationic starch or the aqueous treatment solution of the
second component to be usable for formulating, i.e. emulsifying and/or
stabilizing sizing agent is at most 250 mPas, preferably at most 200 mPas
and more preferably in the range of 100 ¨ 200 mPas. According to an
embodiment of the invention the suitable viscosity may be achieved when the
content of the amphoteric polyacrylamide in said treatment solution is in the
range of 0.7 ¨ 1.0 weight-%.
According to one preferred embodiment of the invention, ASA is emulsified
with cationic starch and the obtained ASA emulsion is combined with an
aqueous treatment solution of the polymer product comprising amphoteric
polyacrylamide prior to addition in to fibre suspension or they are added
separately to fibre suspension.
When ASA is emulsified in cationic starch, cationic starch and ASA may be
present in a weight ratio of 1:1 ¨ 2:1 (dry/dry).
In another embodiment according to the present invention for manufacturing
a paper of board, an aqueous treatment solution of the polymer product
comprising amphoteric polyacrylamide and a hydrophobic internal sizing
agent are added separately to a fibre suspension. They may be added
sequentially or simultaneously but separately. In a typical method, they are
added to the fibre suspension in different points of the manufacturing
process.
The aqueous treatment solution of the polymer product comprising
amphoteric polyacrylamide may be added to the thick stock as a wet end
chemical or it may be added to a thin stock. Thick stock is here understood
as a fibrous stock or furnish, which has consistency of above 20 g/I,
preferably more than 25 g/I, more preferably more than 30 g/I. According to
one embodiment the aqueous treatment solution of the polymer product
comprising amphoteric polyacrylamide is added to fibre suspension having
consistency of above 20 g/I. According to one embodiment, the addition of
the treatment solution of the polymer product comprising amphoteric
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
17
polyacrylamide is located after the stock storage towers, but before thick
stock is diluted in the wire pit (off-machine silo) with short loop white
water.
Preferably the treatment solution of the polymer product comprising
amphoteric polyacrylamide is added to the fibre suspension before a
machine chest, more preferably before a mixing chest, of a paper or board
machine. In an embodiment of the invention at least part of the amphoteric
polyacrylamide is added to the fibre suspension having consistency of above
20 g/I.
The treatment solution of the polymer product comprising amphoteric
polyacrylamide may also be added to a thin stock, i.e. after the point of
thick
stock dilution, similarly as conventional retention polymers. The treatment
solution may be added to a thin stock at any point before a headbox of the
paper or board machine. In an embodiment, at least part of the amphoteric
polyacrylamide is added to the fibre suspension close to a head box, before
or after a (pressure) screen of the paper or board machine. An amount of the
amphoteric polyacrylamide to be added may be remarkably lower when it is
added close to a head box compared to an addition into the thick stock.
In an embodiment an aqueous treatment solution of the polymer product
comprising amphoteric polyacrylamide is added sequentially so that at least
part of the treatment solution is added to the fibre suspension having
consistency of above 20 g/I and last part is added to a thin stock.
According to the invention, a hydrophobic internal sizing agent may also be
added to a thin stock or a thick stock at any suitable point.
In an embodiment of the invention both a hydrophobic internal sizing agent
and an aqueous treatment solution of the polymer product comprising
amphoteric polyacrylamide may be added to a fibre suspension before
dilution of the fibre suspension. It is believed that this embodiment achieves
further improved sizing performance due to enhanced interactions between
the fibres and the hydrophobic internal sizing agent and the amphoteric
polyacrylamide at the higher consistency. In another embodiment of the
invention an aqueous treatment solution of the polymer product comprising
amphoteric polyacrylamide may be added into thick stock just before dilution
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
18
and a hydrophobic internal sizing agent thereafter either to thick stock or
thin
stock.
In one preferred embodiment, an aqueous treatment solution of the polymer
product comprising amphoteric polyacrylamide and a hydrophobic internal
sizing agent are added separately close to each other, i.e. within short
intervals. It is believed that this embodiment achieves further improved
sizing
performance because of improved interaction between the closely added
components.
In an embodiment according to the invention, at least part of the aqueous
treatment solution of the water-soluble polymer product is added to a fraction
of the fibre suspension comprising a broke suspension after a broke tower
and prior to a thickener for broke suspension, and the thickened broke
suspension is combined with other fractions of the fibre suspension. When
broke fraction to be added to the fibre suspension is treated with an aqueous
treatment solution of the polymer product comprising amphoteric
polyacrylamide before a broke thickener, a thickened broke suspension may
comprise more fines with which a hydrophobic internal sizing agent added
afterwards may associate. This may further improve an internal sizing effect.
Consequently, also turbidity and/or hydrophobics content and/or anionic trash
content in the filtrate from the thickener may be decreased, thereby
improving the overall quality of circulating waters in the whole papermaking
process. In addition, an internal sizing effect may be further improved by
adding an aqueous treatment solution of the polymer product comprising
amphoteric polyacrylamide also after a broke tank and/or to a thin stock,
wherein a retention of fines is more efficient and may comprise more the
associated internal sizing agent.
It has been observed that in an embodiment, where a hydrophobic internal
sizing agent is added first to a fibre suspension and then an aqueous
treatment solution of the polymer product comprising amphoteric
polyacrylamide, sizing performance, e.g. Cobb60 value of the paper or board
product may be improved significantly. It is believed that in this embodiment,
a part of the hydrophobic internal sizing agent is retained on fibres, and the
non-retained part interacts with fines and fillers that the amphoteric
polyacrylamide then further retains on the fibres. In another embodiment a
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
19
hydrophobic internal sizing agent may be dosed to thick stock just before
dilution, and an aqueous treatment solution of amphoteric polyacrylamide
may be dosed to thin stock before pressure screen. It has been observed
that sizing performance, e.g. Cobb60 value of the paper or board product may
be improved also by this sequence. Yet in another preferred embodiment a
hydrophobic internal sizing agent and at least part of an aqueous treatment
solution of polymer product comprising amphoteric polyacrylamide are added
to a fibre suspension having consistency of above 20 g/I, and at least part of
the aqueous treatment solution is added to the aqueous fibre suspension
after dilution into thin stock. It is believed that this embodiment achieves
further improved sizing performance, e.g. lower Cobb60 value of the paper or
board product, as the first part(s) of the amphoteric polyacrylamide may
assist in retaining and fixing to the fibres major part of the hydrophobic
internal sizing agent, while the subsequent part(s) of the amphoteric
polyacrylamide may assist in retaining and fixing to the fibres any remaining
hydrophobic internal sizing agent, whether present as free, or bound e.g. to
the fines and fillers present in the fibre suspension.
In some embodiments, a paper or board comprising the internal sizing
system or manufactured according to the present invention may have at least
5 %, preferably at least 8 %, more preferably at least the 10 % lower Cobb60
value compared to an otherwise similar paper or board not comprising the
second component of the internal sizing system. In some embodiments, a
paper or board having a predetermined Cobb60 value and comprising the
internal sizing system or manufactured according to the present invention,
may comprise at least 5 %, preferably at least 10 %, more preferably at least
15 % less of the first component of the internal sizing system, compared to
an otherwise similar paper or board having the same predetermined Cobb6o
value but not comprising the second component of the internal sizing system.
As used herein, by Cobb60 values are meant values measured according to
ISO 535, T441, using e.g. L&W Cobb Sizing Tester.
In a further embodiment of the invention, an emulsion or dispersion of the
hydrophobic internal sizing agent is combined with an aqueous treatment
solution of the polymer product comprising amphoteric polyacrylamide prior
to addition to fibre suspension. It is believed that this achieves further
improved sizing performance due to better interaction between the internal
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
sizing agent and the amphoteric polyacrylamide assisting in its retention and
fixing to the fibres. The combining may be simply carried out by mixing a
separate solutions or streams of an aqueous treatment solution of the
polymer product comprising amphoteric polyacrylamide and a hydrophobic
5 internal sizing agent. In an embodiment, a hydrophobic internal sizing
agent
is formulated with a cationic starch and the obtained emulsion is combined
with an aqueous treatment solution of the polymer product comprising
amphoteric polyacrylamide prior to addition to fibre suspension. Typical
dosage point of the combination of the amphoteric polyacrylamide and the
10 hydrophobic sizing agent may depend on the manufacturing process and the
paper or board to be manufactured.
An amount of the polymer product comprising amphoteric polyacrylamide to
be added may depend on the hydrophobic internal sizing agent which is used
15 in combination with it. A dosage amount of the polymer product
comprising
amphoteric polyacrylamide is typically in the range of 0.1 ¨ 1.5 kg (dry)/ ton
paper or board, or preferably 0.2 ¨ 1 kg (dry)/ ton paper or board. In an
embodiment according to the invention, in which at least part of the polymer
product comprising amphoteric polyacrylamide is added to a fraction of the
20 fibre suspension comprising broke prior to combining the broke fraction
with
other fractions of the fibre suspension, a dosage amount of the polymer
product to be added to the broke fraction may be 0.05 ¨ 0.3 kg (dry)/ton
paper or board. Further, the polymer product may also be added about 0.1 ¨
0.2 kg (dry)/ ton paper or board to a thickened broke suspension prior to
combining it with other fractions of the fibre suspension.
Typically, different internal sizing agents require different dosage amounts.
An amount of ASA to be added may be in the range of 0.2 - 5 kg (dry)/ton
paper or board, preferably 0.7 - 3 kg (dry)/ton paper or board. An amount of
AKD to be added may be in the range of 0.2 - 4 kg (dry)/ton paper or board,
preferably 0.7 - 2 kg (dry)/ton paper or board. An amount of rosin resin to be
added may be in the range of 0.5 - 10 kg (dry)/ton paper or board, preferably
1.5 - 3 kg (dry)/ton paper or board.
A fibre suspension may be any kind of fibre suspension. In the present
context, and as used above, the term "fibre suspension" is understood as an
aqueous suspension, which comprises fibres, preferably recycled fibres, and
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
21
optionally fillers. The water-soluble polymer product comprising amphoteric
polyacrylamide is especially suitable for manufacture of paper and/or board
grades having an ash content before coating, if any, of > 10 %, preferably >
15 %, more preferably > 20 %. Standard ISO 1762, temperature 525 C is
used for ash content measurements. For example, the fibre suspension may
comprise at least 5 %, preferably 10 ¨ 30 %, more preferably 11 ¨ 19 % of
mineral filler. The amount of mineral filler is calculated by drying the fibre
suspension, and the ash content is measured by using standard ISO 1762, at
temperature 525 C. Mineral filler may be any filler conventionally used in
paper and board making, such as ground calcium carbonate, precipitated
calcium carbonate, clay, talc, gypsum, titanium dioxide, synthetic silicate,
aluminium trihydrate, barium sulphate, magnesium oxide or any of their
combinations.
An internal sizing system of the invention performs over a broad pH range of
the fibre suspension. A pH of the fibre suspension may be e.g. 4 - 10, but
typically pH is in the range of 5 - 8. While the optimum pH range for each
hydrophobic internal sizing agent may be narrower, it is believed that due to
the improved retention and fixing provided by the specified amphoteric
polyacrylamide, the usable pH ranges of each sizing agent may be
broadened.
In an embodiment of the invention the fibre suspension may comprise
recycled fibre material. According to one embodiment the fibre suspension
comprises at least 50 weight-%, preferably at least 60 weight-%, more
preferably at least 70 weight-%, of recycled fibre material, based on dry
paper or paperboard. In some embodiments the fibre suspension may
comprise even > 80 weight-%, or 100 weight-%, of fibres originating from
recycled fibre materials.
According to one embodiment the fibre suspension has a conductivity of at
least 1.5 mS/cm, preferably at least 2.0 mS/cm, more preferably at least 3.0
mS/cm, measured at the headbox of the paper or board machine. Elevated
conductivity is typical for fibre suspension comprising recycled fibres and/or
closed papermaking process. The polymer product comprising amphoteric
polyacrylamide can be used even at elevated conductivity, without significant
decrease in effectivity in retention of the hydrophobic internal sizing
agents.
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
22
An internal sizing system according to the present invention performs also
over wide anionic charge range of the fibre suspension, even close to zero
where typical cationic additives may cause overcationization and foaming.
Typical performance range may be -0.1 - -1.5 meq/L of the fibre suspension,
but the internal sizing system according to the present invention performs
well even at fibre suspension having anionic charge of -15 meq/L, such as in
neutral sulfite semi-chemical pulp. The anionic charge of the fibre suspension
may be measured by Mutek Particle Charge Detector.
According to one embodiment of the invention the fibre suspension
comprises fibres obtained by kraft and/or mechanical pulping process(es). In
one preferred embodiment, a fibre suspension may be unbleached kraft or
mechanical pulp. In these fibre suspension, particularly good performance of
the internal sizing system according to the present invention has been
observed compared to conventional sizing systems, which may be due to the
inherent high load of colloidal material and interfering substances of these
fibre suspensions that the present sizing system is able to control. An
internal
sizing system according to the invention performs even in 100 weight-%
unbleached kraft and/or mechanical or CTMP fibre suspension. According to
an embodiment of the invention a fibre suspension may comprise kraft and
recycled fibre material in a weight ratio of 50:50.
According to one embodiment an internal sizing system is used for improving
retention of the hydrophobic internal sizing agents in manufacture of paper or
board. The board may be selected from liner, fluting, gypsum board liner, wall
paper, core board, folding boxboard (FBB), white lined chipboard (WLC),
solid bleached sulphate (SBS) board, solid unbleached sulphate (SUS) board
or liquid packaging board (LPB) such as cup stock. The boards may be
based 100 (:)/0 on primary fibres, 100 (:)/0 on recycled fibres, or to any
possible
blend between the primary fibres and the recycled fibres. An internal sizing
system according to the invention is also suitable for use in manufacturing of
fine paper grades; both uncoated and coated fine paper.
An internal sizing system and a method according to the invention is also
suitable for multi-layered board production. By multi-layered board production
is meant production of board comprising at least two layers of fibres. Such
multi-layered board may be manufactured by delivering aqueous fibre
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
23
suspension to a multi-layer headbox, draining the aqueous fibre suspension
on a wire screen to form a wet web of paper or paperboard, and pressing and
drying the wet web to obtain a multi-layered web of board. Alternatively, the
multi-layered board may be manufactured by delivering aqueous fibre
suspension(s) to at least two headboxes, draining the aqueous fibre
suspension(s) on at least two wire screens to form wet webs of paper or
paperboard, interposing the wet fibre webs, and pressing and drying the
interposed wet web to obtain a multi-layered web of board. In the multi-
layered products, an internal sizing system according to the invention
comprising amphoteric polyacrylamide and hydrophobic internal sizing agent
are typically added to same fibre suspension forming one or more of the
layers of the multi-layered board product. The one or more layers may be a
middle layer or any of the surface layers of the product. According to an
embodiment of the invention amphoteric polyacrylamide and hydrophobic
internal sizing agent are added to all layers.
EXPERIMENTAL
Some embodiments of the invention are described in the following non-
limiting examples.
Polymer Example: General description of the polymer product preparation
Preparation of monomer solution for the amphoteric polyacrylamide
Monomer solution is prepared by mixing 248.3 g of 50 (:)/0 acrylamide
solution,
0.01 g of 40 (:)/0 DTPA Na-salt solution, 2.9 g of sodium gluconate, 4.4 g of
dipropylene glycol, 1.9 g of adipic acid, and 7.2 g of citric acid in a
temperature controlled laboratory glass reactor at 20 ¨ 25 C. The mixture is
stirred until solid substances are dissolved. To the solution is added 32.6 g
of
80 (:)/0 ADAM-Cl. pH of the solution is adjusted to 3.0 with citric acid, and
2.8 g
of acrylic acid is added to the solution. pH is adjusted to be 2.5 ¨ 3Ø
Preparation of dry polymer product
After the monomer solution is prepared according to the above description,
the monomer solution is purged with nitrogen flow in order to remove oxygen.
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
24
An initiator is added to the monomer solution. The initiator solution is 4 ml
of
6 (:)/0 2-hydroxy-2-methylpropiophenone in polyethylene glycol-water (1:1 by
weight) solution. The monomer solution is placed on a tray to form a layer of
about 1 cm under UV-light. UV-light is mainly on the range 350 - 400 nm, for
example light tubes Philips Actinic BL TL 40W can be used. Intensity of the
light is increased as the polymerisation proceeds to complete the
polymerisation. The first 10 minutes the light intensity is 550 pW/cm2, and
following 30 minutes it is 2000 pW/cm2. The obtained gel is run through an
extruder and dried to moisture content less than 10 "Yo at temperature of 60
C. The dried polymer is ground and sieved to particle size 0.5 ¨ 1.0 mm.
Intrinsic viscosity of the polymer product was determined by Ubbelohde
capillary viscometer in 1 M NaCI at 25 C. Polymer product was dissolved in
1 M NaCI and a series of dilutions at suitable concentrations ranging from
0.01 to 0.5 g/dI for viscosity determinations. pH of the polymer solution for
capillary viscosity determination was adjusted to 2.7 by formic acid to avoid
impact of probable polyion complexation for viscosity. Molecular weights
were calculated using "K" and "a" parameters of polyacrylamide. The value of
parameter "K" is 0.0191 ml/g and the value of parameter "a" is 0.71.
Determined intrinsic viscosity was 9.9 dl/g and calculated molecular weight 4
400 000 g/mol.
The obtained polymer product comprising amphoteric polyacrylamide
containing 7 mol-`)/0 ADAM-CI, 2 mol-`)/0 acrylic acid and 91 mol-% acrylamide
is used in the following Application Examples.
Application Example 1
ASA retention in liquid packaging board machine is investigated in laboratory.
An aqueous treatment solution of the polymer product comprising amphoteric
polyacrylamide is combined with ASA-starch (starch use herein is cationic
starch) emulsion before introducing to a fibre suspension. As references,
ASA-starch emulsion is used without co-addition of any synthetic polymer,
and with co-addition of a conventional cationic inorganic coagulant
polyaluminium chloride (PAC), and a cationic glyoxylated polymer (GPAM).
The GPAM used is charge density of about 1.8 meq/g (dry).
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
Laboratory method:
Bleached chemical pulp is taken from a 2-ply board machine chest of the top
ply and diluted to 1 weight-% with clear filtrate water to obtain a pulp
sample.
Pulp sample amount is 300 ml. 9 ml of ASA-starch emulsion is taken with 20
5 ml
syringe. 0.1 weight-% dry content polymer solutions (dosage level 330 g/t
as dry) are added to syringe and mixed in the syringe. Mixture of ASA-starch
emulsion and polymer is added to 300 ml fibre suspension sample. After
chemical addition fibre sample is mixed 60 s with lab mixer at 700 rpm. After
mixing sample is vacuum filtered with Buchner (diameter ¨15 cm) included
10 400 pm
polymer wire. Sample filtrate (20 I) is diluted with distilled water
(980 I) and fluorescent colouring agent (20 I) is added. Flow cytometric
measurement is carried out for diluted sample filtrates using SL Blue device
supplied by Partec GmbH. Also sample of ASA-starch emulsion without fibre
suspension is measured, to identify the location of ASA-particle population in
15 the
measurement data. The amount of total hydrophobic particles and ASA-
particles are measured and calculated from diluted filtrate samples. The
results are presented in Table 1.
Table 1. The amount of unretained total hydrophobics and ASA-particles in
20 sample filtrates.
Size emulsion and Total
Reduction-% Unretained Reduction-
co-additive used unretained of total ASA (:)/0
of ASA
hydrophobic hydrophobics particles, compared
particles, compared to count/ml to Ref.
count/ml Ref.
Ref.(ASA-starch) 6534500 n.a. 1037000 n.a.
ASA-starch + PAC 5400500 17 % 987000 4.8 %
ASA-starch + 4678250 28 % 770750 26 %
GPAM
ASA-starch + 3961500 39 % 172750 83 %
amphoteric PAM
Application Example 2
25 In this
example a 2-layer Fourdrinier machine producing liner paper is run
with ASA addition of 2.5 kg/t paper to base ply thick stock into machine
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
26
chest, the stock comprising unbleached kraft and OCC in weight ratio of
50:50. Thereafter amphoteric polyacrylamide as specified in the claims is
added to the base ply thick stock, to the outlet of the machine chest, in
amounts of 0.3 ¨ 0.6 kg/t paper, while continuing the same ASA dosage. As
a result, Cobb60 value is improved from 29 to 22 g/m2 as shown in Table 2.
Chemicals in base ply thick stock and dosage point:
- ASA size 2.5 kg/t, machine chest
- Cationic starch 5 kg/t, machine chest
- Alum 3 kg/t, machine chest
- Retention grade CPAM and silica, before and after screen
Wet end conditions in base ply are pH 7, conductivity 2500 pS/cm, anionic
charge -350 pekv/I, and zeta potential -10 mV.
Table 2. Cobb60 improvement with different dosages of the specified
amphoteric polyacrylamide
Machine Amphoteric polyacrylamide Cobb6o,
reel kg/t g/m2
1 0 29
2 0.3 27
3 0.45 26
4 0.6 24
6 0.6 23
8 0.6 22
9 0 26
Application Example 3
In this example a 2-layer 1 fourdrinier machine producing kraftliner from
100 "Yo unbleached kraft fibres is run with ASA addition to thick stock
providing to the paper a target Cobb60 value. Thereafter amphoteric
polyacrylamide as specified in the claims is started to be added to thick
stock. Paper's Cobb60 value is monitored and ASA dosage is decreased to
maintain the target Cobb60 value. Target Cobb60 value is steady with 25 ¨ 30
"Yo lower ASA dosage, compared to not using the amphoteric polyacrylamide.
CA 03079693 2020-04-08
WO 2019/086761
PCT/F12018/050792
27
Application Example 4
In this example folding box board is produced using CTMP and broke in the
middle ply furnish. ASA is added to middle ply furnish, pH 7, providing to the
board a target Cobb60 value. Thereafter amphoteric polyacrylamide as
specified in the claims is added 200 ¨ 400 g/t board to thin stock before
pressure screen. Board's Cobb60 value is monitored and ASA dosage
decreased to maintain the target Cobb60 value. Target Cobb60 value is steady
with 12 % lower ASA dosage, compared to not using the amphoteric
polyacrylamide. At the same time less deposits are observed on the
machinery, resulting in improved runnability.
